Grain-oriented electrical steel sheet and method for manufacturing same

ABSTRACT

Provided are a grain-oriented electrical steel sheet with low iron loss even when including at least one grain boundary segregation element among Sb, Sn, Mo, Cu, and P, and a method for manufacturing the same. In our method, Pr is controlled to satisfy Pr≤−0.075T+18, where T&gt;10, 5&lt;Pr, T (hr) is the time required after final annealing to reduce the temperature of a secondary recrystallized sheet from 800° C. to 400° C., and Pr (MPa) is the line tension on the secondary recrystallized sheet during flattening annealing. As a result, a grain-oriented electrical steel sheet in which iron loss is low and a dislocation density near crystal grain boundaries of the steel substrate is 1.0×1013 m−2 or less can be obtained even when the grain-oriented electrical steel sheet contains at least one of Sb, Sn, Mo, Cu, and P.

TECHNICAL FIELD

This disclosure relates to a grain-oriented electrical steel sheet thathas low iron loss and is suitable as an iron core material in atransformer, and to a method for manufacturing the same.

BACKGROUND

A grain-oriented electrical steel sheet is a soft magnetic material usedas an iron core material of transformers, generators, and the like, andhas a crystal microstructure in which the <001> orientation, which is aneasy magnetization axis of iron, is accorded with the rolling directionof the steel sheet. Such a crystal microstructure is formed bypreferentially causing the growth of giant crystal grains in {110}<001>orientation, which is called Goss orientation, when final annealing forsecondary recrystallization is performed in the process of manufacturingthe grain-oriented electrical steel sheet.

It has been common practice in manufacturing grain-oriented electricalsteel sheets to use precipitates called inhibitors during finalannealing to cause secondary recrystallization of crystal grains withthe Goss orientation. Examples of this method that have been put intopractical use include a method for using AlN and MnS and a method forusing MnS and MnSe. While requiring the slab to be reheated to atemperature of 1300° C. or higher, these methods for using inhibitorsare extremely useful for stably causing growth of secondaryrecrystallized grains.

Furthermore, in order to reinforce the action of these inhibitors, amethod for using Pb, Sb, Nb, and Te and a method for using Zr, Ti, B,Nb, Ta, V, Cr, and Mo are also known. JP 3357615 B2 (PTL 1) discloses amethod for using Bi, Sb, Sn, and P, which are grain boundary segregationelements, in addition to the use of nitrides as inhibitors. JP 5001611B2 (PTL 2) discloses a method for obtaining good magnetic properties byusing Sb, Nb, Mo, Cu, and Sn, which are elements that precipitate atgrain boundaries, even when manufacturing at a thinner slab thicknessthan normal.

CITATION LIST Patent Literature

-   PTL 1: JP 3357615 B2-   PTL 2: JP 5001611 B2-   PTL 3: JP 2012-177162 A-   PTL 4: JP 2012-36447 A

SUMMARY Technical Problem

In recent years, magnetic properties have increasingly improved, andthere is demand for manufacturing of grain-oriented electrical steelsheets that stably achieve a high level of magnetic properties. However,even when adding at least one of Sb, Sn, Mo, Cu, and P, which are grainboundary segregation elements, in order to improve magnetic properties,there has been a significant problem in that the magnetic properties donot actually improve, and low iron loss cannot be obtained.

Therefore, it would be helpful to provide a grain-oriented electricalsteel sheet with low iron loss even when including at least one of Sb,Sn, Mo, Cu, and P, which are grain boundary segregation elements, and amethod for manufacturing the same.

Solution to Problem

In general, when improving magnetic properties by using precipitatesthat are called inhibitors during the manufacturing process, theseprecipitates block displacement of the domain wall in the finishedproduct, causing the magnetic properties to deteriorate. Therefore,final annealing is performed under conditions that allow N, S, Se, andthe like, which are precipitate forming elements, to be discharged fromthe steel substrate either to the coating or outside of the system. Inother words, the final annealing is performed for between several hoursand several tens of hours at a high temperature of approximately 1200°C. under an atmosphere mainly composed of H₂. By this treatment, the N,S, and Se in the steel substrate diminish to the analytical limit orbelow, and good magnetic properties can be ensured in the finishedproduct, without formation of precipitates.

On the other hand, when at least one of Sb, Sn, Mo, Cu, and P, which aregrain boundary segregation elements, is included in the slab, theseelements are not displaced in the coating or ejected from the systemduring the final annealing. Accordingly, we thought that these elementsmight have some sort of effect that makes magnetic properties unstableduring flattening annealing. According to our observations, manydislocations occur near crystal grain boundaries in a grain-orientedelectrical steel sheet with degraded magnetic properties. The reason isthought to be that Sb, Sn, Mo, Cu, and P segregate at grain boundariesduring the cooling process after final annealing.

As a result of conducting intensive study to solve this issue, wediscovered that in relation with the time during which a secondaryrecrystallized sheet is retained in a certain temperature range afterfinal annealing, it is effective to control the line tension during thesubsequent flattening annealing. It is thought that, as a result, theoccurrence of dislocations near crystal grain boundaries of the steelsubstrate can be effectively suppressed after flattening annealing andthat the degradation in magnetic properties occurring due to blockage ofdomain wall displacement by dislocations can be suppressed.

Based on the above findings, the primary features of our steel sheetsand methods for manufacturing the same are described below.

[1] A grain-oriented electrical steel sheet comprising; a steelsubstrate and a forsterite film on the surface of a steel substrate,wherein

the steel substrate comprises a chemical composition containing(consisting of), in mass %, Si: 2.0% to 8.0% and Mn: 0.005% to 1.0% andat least one of Sb: 0.010% to 0.200%, Sn: 0.010% to 0.200%, Mo: 0.010%to 0.200%, Cu: 0.010% to 0.200%, and P: 0.010% to 0.200%, and thebalance consisting of Fe and incidental impurities; and

a dislocation density near crystal grain boundaries of the steelsubstrate is 1.0×10¹³ m⁻² or less.

[2] The grain-oriented electrical steel sheet of [1], wherein thechemical composition further contains, in mass %, at least one of Ni:0.010% to 1.50%, Cr: 0.01% to 0.50%, Bi: 0.005% to 0.50%, Te: 0.005% to0.050%, and Nb: 0.0010% to 0.0100%.

[3] A method for manufacturing a grain-oriented electrical steel sheet,the method comprising, in sequence:

subjecting a steel slab to hot rolling to obtain a hot rolled sheet, thesteel slab comprising a chemical composition containing (consisting of),in mass %, Si: 2.0% to 8.0% and Mn: 0.005% to 1.0% and at least one ofSb: 0.010% to 0.200%, Sn: 0.010% to 0.200%, Mo: 0.010% to 0.200%, Cu:0.010% to 0.200%, and P: 0.010% to 0.200%, and the balance consisting ofFe and incidental impurities;

subjecting the hot rolled sheet to hot band annealing as required;

subjecting the hot rolled sheet to cold rolling once or cold rollingtwice or more with intermediate annealing in between, to obtain a coldrolled sheet with a final sheet thickness;

subjecting the cold rolled sheet to primary recrystallization annealingto obtain a primary recrystallized sheet;

applying an annealing separator onto a surface of the primaryrecrystallized sheet and then subjecting the primary recrystallizedsheet to final annealing for secondary recrystallization, to obtain asecondary recrystallized sheet that has a forsterite film on a surfaceof a steel substrate; and

subjecting the secondary recrystallized sheet to flattening annealingfor 5 seconds or more and 60 seconds or less at a temperature of 750° C.or higher;

wherein during the flattening annealing, Pr is controlled to satisfy thefollowing conditional Expression (1), so that a dislocation density nearcrystal grain boundaries of the steel substrate is 1.0×10¹³ m⁻² or less:Pr≤−0.075T+18(where T>10,5<Pr)  (1)

where Pr (MPa) is a line tension on the secondary recrystallized sheet,and T (hr) is a time required after the final annealing to reduce atemperature of the secondary recrystallized sheet from 800° C. to 400°C.

[4] The method for manufacturing a grain-oriented electrical steel sheetof [3], wherein during cooling of the secondary recrystallized sheetafter the final annealing, the secondary recrystallized sheet is heldfor 5 hours or longer at a predetermined temperature from 800° C. to400° C.

[5] The method for manufacturing a grain-oriented electrical steel sheetof [3] or [4], wherein the chemical composition contains, in mass %, Sb:0.010% to 0.100%, Cu: 0.015% to 0.100%, and P: 0.010% to 0.100%.

[6] The method for manufacturing a grain-oriented electrical steel sheetof any one of [3] to [5], wherein the chemical composition furthercontains, in mass %, at least one of Ni: 0.010% to 1.50%, Cr: 0.01% to0.50%, Bi: 0.005% to 0.50%, Te: 0.005% to 0.050%, and Nb: 0.0010% to0.0100%.

[7] The method for manufacturing a grain-oriented electrical steel sheetof any one of [3] to [6], wherein the chemical composition furthercontains, in mass %, C: 0.010% to 0.100%, Al: 0.01% or less, N: 0.005%or less, S: 0.005% or less, and Se: 0.005% or less.

[8] The method for manufacturing a grain-oriented electrical steel sheetof any one of [3] to [6], wherein the chemical composition furthercontains, in mass %,

C: 0.010% to 0.100%; and

at least one of

-   -   (i) Al: 0.010% to 0.050% and N: 0.003% to 0.020%, and    -   (ii) S: 0.002% to 0.030% and/or Se: 0.003% to 0.030%.

The line tension during flattening annealing is referred to in JP2012-177162 A (PTL 3) and JP 2012-36447 A (PTL 4), but these techniquesare for preventing degradation of the tensile tension of forsterite filmand differ substantially from this disclosure, which proposes to reducedislocations in the steel substrate. We focus on controlling therelationship we newly discovered between the time required after finalannealing to reduce the temperature of a secondary recrystallized sheetfrom 800° C. to 400° C. (hereinafter also referred to as the “retentiontime from 800° C. to 400° C. after final annealing”) and the linetension during flattening annealing.

Advantageous Effect

Since the dislocation density near crystal grain boundaries of the steelsubstrate is 1.0×10¹³ m⁻² or less, our grain-oriented electrical steelsheet has low iron loss even when containing at least one of Sb, Sn, Mo,Cu, and P, which are grain boundary segregation elements.

Our method for manufacturing a grain-oriented electrical steel sheetoptimizes the line tension Pr (MPa) on the secondary recrystallizedsheet during flattening annealing in relation to the retention time T(hr) from 800° C. to 400° C. after final annealing. Therefore, agrain-oriented electrical steel sheet in which iron loss is low and thedislocation density near crystal grain boundaries of the steel substrateis a low value of 1.0×10¹³ m⁻² or less can be obtained even when thegrain-oriented electrical steel sheet contains at least one of Sb, Sn,Mo, Cu, and P.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 illustrates the relationship between the line tension Pr (MPa) onthe secondary recrystallized sheet during flattening annealing and theiron loss W_(17/50) (W/kg) of the product sheet in Experiment 1;

FIG. 2 is a TEM image near the grain boundary of the product sheet whenthe line tension Pr is 16 MPa using steel slab B in Experiment 1;

FIG. 3 is a TEM image near the grain boundary of the product sheet whenthe line tension Pr is 8 MPa using steel slab B in Experiment 1;

FIG. 4 represents the effects on the iron loss W_(17/50) (W/kg) of theproduct sheet due to the retention time T (hr) from 800° C. to 400° C.after final annealing and the line tension Pr (MPa) on the secondaryrecrystallized sheet during flattening annealing in Experiment 2; and

FIG. 5 represents the effects on the dislocation density (m⁻²) nearcrystal grain boundaries of the steel substrate of the product sheet dueto the retention time T (hr) from 800° C. to 400° C. after finalannealing and the line tension Pr (MPa) on the secondary recrystallizedsheet during flattening annealing in Experiment 2.

DETAILED DESCRIPTION

The following describes the experiments by which the present disclosurehas been completed.

<Experiment 1>

A steel slab A containing, in mass %, C: 0.063%, Si: 3.35%, Mn: 0.09%,S: 0.0032%, N: 0.0020%, and sol.Al: 0.0044%, and a steel slab Bcontaining, in mass %, C: 0.065%, Si: 3.33%, Mn: 0.09%, S: 0.0030%, N:0.0028%, sol.Al: 0.0048%, and Sb: 0.037% were manufactured by continuouscasting and subjected to slab reheating to 1200° C. Subsequently, thesesteel slabs were subjected to hot rolling and finished to hot rolledsheets with a sheet thickness of 2.0 mm. Thereafter, the hot rolledsheets were subjected to hot band annealing for 40 seconds at 1050° C.and then finished to cold rolled sheets with a sheet thickness of 0.23mm by cold rolling. Furthermore, the cold rolled sheets were subjectedto primary recrystallization annealing, which also served asdecarburization annealing, for 130 seconds at 840° C. in a 50% H₂/50% N₂wet atmosphere with a dew point of 60° C. to obtain primaryrecrystallized sheets. Subsequently, an annealing separator primarilycomposed of MgO was applied onto a surface of the primary recrystallizedsheets and then the primary recrystallized sheets were subjected tofinal annealing for secondary recrystallization by holding for 10 hoursat 1200° C. in an H₂ atmosphere, to obtain a secondary recrystallizedsheet. The retention time T (hr) from 800° C. to 400° C. after the finalannealing was set to 40 hours. In this disclosure, the “temperature ofthe secondary recrystallized sheet” refers to the temperature measuredat an intermediate position between the innermost turn and the outermostturn on the edge face of a coil of the secondary recrystallized sheet(the edge face being the lowermost portion when the coil is stood onend).

Furthermore, for shape adjustment, the secondary recrystallized sheetswere subjected to flattening annealing for 30 seconds at 830° C. toobtain product sheets. At this time, the line tension Pr (MPa) on thesecondary recrystallized sheets was changed to a variety of values. Inthis disclosure, the “line tension” refers to the tensile tensionapplied to the secondary recrystallized sheet mainly in order to preventmeandering during sheet passing through a continuous annealing furnaceand is controlled by bridle rolls before and after the annealingfurnace.

The iron loss W_(17/50) (iron loss upon 1.7 T excitation at a frequencyof 50 Hz) of the resulting product sheet was measured with the methodprescribed by JIS C2550. FIG. 1 illustrates the results. These resultsshow that in the case of the steel slab B containing Sb, the iron lossW_(17/50) of the product sheet could be reduced sufficiently, ascompared to the steel slab A, when the line tension Pr was set to 15 MPaor less. For both steel slabs A and B, creep deformation occurred in theproduct sheet at a line tension of 18 MPa, which was thought to be thereason for serious degradation in the magnetic properties.

Upon performing component analysis on the steel substrate of theseproduct sheets, the C content was reduced to approximately 12 mass ppm,and the S, N, and sol.Al contents changed to less than 4 mass ppm (belowthe analytical limit) for both steel slabs A and B, but the Si, Mn, andSb contents were nearly equivalent to the contents in the slabs. Thecomponent analysis of the steel substrates was performed once theproduct sheets were dried after being immersed for two minutes in a 10%HCl aqueous solution at 80° C. to remove the forsterite film of theproduct sheets. These results show that sulfides and nitrides thatdegrade magnetic properties did not precipitate, indicating thatprecipitates could not easily be the cause of degradation.

Next, in the case of the steel slab B that includes the grain boundarysegregation element Sb, the area near crystal grain boundaries of thesteel substrate of the product sheet was observed using a transmissionelectron microscope (TEM) (JEM-2100F produced by JEOL) in order todiscover why iron loss of the product sheet reduces as the line tensionPr is decreased. As a result, it became clear that when the line tensionPr is set to 16 MPa, several dislocations are present at and near thegrain boundary, as illustrated in FIG. 2. The area of this field was 2.2μm², and 5 dislocations were observable. Therefore, the dislocationdensity in this observation field was approximately 2.3×10¹² m⁻², andthe average of 10 fields exceeded 1.0×10¹³ m⁻². On the other hand, whenthe line tension Pr was set to 8 MPa, there were almost no dislocationspresent, and the dislocation density in this observation field wascalculated as 0, as illustrated in FIG. 3. Hence, it is presumed thatwhen the grain boundary segregation element Sb is included in the steelslab, dislocations easily accumulate at the grain boundary if the linetension Pr is high, leading to degradation in magnetic properties.

During final annealing of the grain-oriented electrical steel sheet,batch annealing is typically performed with the primary recrystallizedsheets in a coiled state. Therefore, after holding at approximately1200° C., secondary recrystallized sheets are cooled. Note that theretention time from 800° C. to 400° C. after final annealing can bechanged and controlled by controlling the flow of the atmosphere.

Accordingly, segregation of a grain boundary segregation element to thegrain boundary is freed during final annealing, and the grain boundarysegregation element dissolves in the crystal grains, but if thesubsequent cooling process is lengthy, then the grain boundarysegregation element may segregate to the grain boundary at that time. Inother words, it is thought that if the cooling rate is slow, the amountof segregation increases, and magnetic properties further degrade duringthe subsequent flattening annealing if the line tension Pr is high.Therefore, we examined the effect on the magnetic properties due to theretention time at the time of final annealing from 800° C. to 400° C.and the line tension Pr during the flattening annealing.

<Experiment 2>

A steel slab C containing, in mass %, C: 0.048%, Si: 3.18%, Mn: 0.14%,S: 0.0020%, N: 0.0040%, sol.Al: 0.0072%, and Sb: 0.059% was manufacturedby continuous casting and subjected to slab reheating to 1220° C.Subsequently, the steel slab was subjected to hot rolling and finishedto a hot rolled sheet with a sheet thickness of 2.2 mm. Thereafter, thehot rolled sheet was subjected to hot band annealing for 30 seconds at1025° C. and then finished to a cold rolled sheet with a sheet thicknessof 0.27 mm by cold rolling. Furthermore, the cold rolled sheet wassubjected to primary recrystallization annealing, which also served asdecarburization annealing, for 100 seconds at 850° C. in a 50% H₂/50% N₂wet atmosphere with a dew point of 62° C. to obtain a primaryrecrystallized sheet. Subsequently, an annealing separator primarilycomposed of MgO was applied onto a surface of the primary recrystallizedsheet and then the primary recrystallized sheet was subjected to finalannealing for secondary recrystallization by holding for 10 hours at1200° C. in an H₂ atmosphere, to obtain a secondary recrystallizedsheet. At this time, the cooling rate after the final annealing wasvaried to change the retention time T (hr) from 800° C. to 400° C. to avariety of values.

Furthermore, for shape adjustment, the secondary recrystallized sheetwas subjected to flattening annealing for 15 seconds at 840° C. toobtain a product sheet. At this time, the line tension Pr (MPa) on thesecondary recrystallized sheet was changed to a variety of values. At aline tension Pr of 5 MPa or less, however, the secondary recrystallizedsheet meandered, and regular sheet passing could not be performed.Therefore, the minimum line tension was set above 5 MPa.

The iron loss W_(17/50) of the resulting product sheet was measured withthe method prescribed by JIS C2550. FIG. 4 illustrates the results.These results show that an increase in length of the retention time Tfrom 800° C. to 400° C. after final annealing decreases the upper limitof the line tension Pr during the flattening annealing at which low ironloss is expressed.

One possible explanation is that, as considered in Experiment 1, in astate in which the grain boundary segregation element is segregated atthe grain boundary, the magnetic properties may degrade as a result ofaccumulation of dislocations at grain boundaries due to application ofline tension. In other words, it could be that due to final annealing at1200° C. for an extended time, the grain boundary segregation elementalso redissolves in the grains and then resegregates at the grainboundaries during the cooling process. A reasonable explanation is thatat this time, as the retention time grows longer in the temperaturerange of 800° C. to 400° C., in which segregation easily occurs andatoms also easily diffuse, the amount of segregation at the grainboundaries increases, and dislocations occurring near the grainboundaries also increase during the flattening annealing, causing theupper limit of the line tension to decrease. This explanation issupported by FIG. 5.

In this way, in a method for manufacturing a grain-oriented electricalsteel sheet that includes a grain boundary segregation element in asteel slab, we succeeded in effectively reducing the dislocation densitynear crystal grain boundaries of the steel substrate of a product sheetto 1.0×10¹³ m⁻² or less and in preventing degradation of magneticproperties by controlling the line tension Pr, in relation with theretention time T from 800° C. to 400° C. after final annealing, duringthe subsequent flattening annealing.

The following describes our grain-oriented electrical steel sheet indetail. First, the reasons for limiting the contents of the componentsof the chemical composition will be explained. Unless otherwisespecified, all concentrations stated herein as “%” and “ppm” refer tomass % and mass ppm.

Si: 2.0% to 8.0%

Si is a necessary element for increasing the specific resistance of agrain-oriented electrical steel sheet and for reducing the iron loss.This effect is not sufficient if the Si content is less than 2.0%, butupon the content exceeding 8.0%, the workability reduces, making rollingfor steel manufacturing difficult. Therefore, the Si content is set tobe 2.0% or more and 8.0% or less. The Si content is preferably 2.5% ormore and is preferably 4.5% or less.

Mn: 0.005% to 1.0%

Mn is an element necessary for improving the hot workability of steel.This effect is not sufficient if the Mn content is less than 0.005%, butupon the content exceeding 1.0%, the magnetic flux density of theproduct sheet reduces. Therefore, the Mn content is set to be 0.005% ormore and 1.0% or less. The Mn content is preferably 0.02% or more and ispreferably 0.30% or less.

In this disclosure, in order to improve magnetic properties, it isnecessary for the steel sheet to include at least one of Sb, Sn, Mo, Cu,and P, which are grain boundary segregation elements. The effect ofimproving magnetic properties is limited when the added amount of eachelement is less than 0.010%, but when the added amount exceeds 0.200%,the saturation magnetic flux density decreases, canceling out the effectof improving magnetic properties. Therefore, the content of each elementis set to be 0.010% or more and 0.200% or less. The content of eachelement is preferably 0.020% or more and is preferably 0.100% or less.In order to prevent the steel sheet from becoming brittle, the Sn and Pcontents is preferably 0.020% or more and is preferably 0.080% or less.The effect of improving magnetic properties is extremely high if thesteel sheet simultaneously contains Sb: 0.010% to 0.100%, Cu: 0.015% to0.100%, and P: 0.010% to 0.100%.

The balance other than the aforementioned components consists of Fe andincidental impurities, but the steel sheet may optionally contain thefollowing elements.

In order to reduce iron loss, the steel sheet may contain at least oneof Ni: 0.010% to 1.50%, Cr: 0.01% to 0.50%, Bi: 0.005% to 0.50%, Te:0.005% to 0.050%, and Nb: 0.0010% to 0.0100%. If the added amount ofeach element is less than the lower limit, the effect of reducing ironloss is small, whereas exceeding the upper limit leads to a reduction inmagnetic flux density and degradation of magnetic properties.

Here, even when C is intentionally contained in the steel slab, as aresult of decarburization annealing the amount of C is reduced to be0.005% or less, a level at which magnetic aging does not occur.Therefore, even when contained in this range, C is considered anincidental impurity.

Our grain-oriented electrical steel sheet has a dislocation density nearcrystal grain boundaries of the steel substrate of 1.0×10¹³ m⁻² or less.Dislocations cause a rise in iron loss by blocking domain walldisplacement. By having a low dislocation density, however, ourgrain-oriented electrical steel sheet has low iron loss. The dislocationdensity is preferably 5.0×10¹² m⁻² or less. It is thought that fewerdislocations are better, and therefore the lower limit is zero. In thiscontext, “near grain boundaries” is defined as a region with 1 m of agrain boundary. The “dislocation density near crystal grain boundaries”in this disclosure was calculated as follows. First, the product sheetwas immersed for 3 minutes in a 10% HCl aqueous solution at 80° C. toremove the film and was then chemically polished to produce a thin filmsample. The areas near grain boundaries of this sample were observedusing a transmission electron microscope (JEM-2100F produced by JEOL) at50,000× magnification, and the number of dislocations near the grainboundaries in the field of view was divided by the field area. Theaverage for 10 fields was then taken as the “dislocation density.”

Next, the method of manufacturing our grain-oriented electrical steelsheet will be described. Within the chemical composition of the steelslab, the elements Si, Mn, Sn, Sb, Mo, Cu, and P and the optionalelements Ni, Cr, Bi, Te, and Nb are as described above. The content ofthese elements does not easily vary during the sequence of processes.Therefore, the amounts are controlled at the stage of componentadjustment in the molten steel.

The balance other than the aforementioned components in the steel slabconsists of Fe and incidental impurities, but the following elements mayoptionally be contained.

C: 0.010% to 0.100%

C has the effect of strengthening grain boundaries. This effect issufficiently achieved if the C content is 0.010% or greater, and thereis no risk of cracks in the slab. On the other hand, if the C content is0.100% or less, then during decarburization annealing, the C content canbe reduced to 0.005 mass % or less, a level at which magnetic aging doesnot occur. Therefore, the C content is preferably set to be 0.010% ormore and is preferably set to 0.100% or less. The C content is morepreferably 0.020% or more and is more preferably 0.080% or less.

Furthermore, as inhibitor components, the steel slab may contain atleast one of (i) Al: 0.010% to 0.050% and N: 0.003% to 0.020%, and (ii)S: 0.002% to 0.030% and/or Se: 0.003% to 0.030%. When the added amountof each component is the lower limit or greater, the effect of improvingmagnetic flux density by inhibitor formation is sufficiently achieved.By setting the added amount to be the upper limit or lower, thecomponents are purified from the steel substrate during final annealing,and iron loss is not reduced. When adopting a technique to improvemagnetic flux density in an inhibitor free chemical composition,however, these components need not be contained. In this case,components are suppressed to the following contents: Al: 0.01% or less,N: 0.005% or less, S: 0.005% or less, and Se: 0.005% or less.

Molten steel subjected to a predetermined component adjustment asdescribed above may be formed into a steel slab by regular ingot castingor continuous casting, or a thin slab or thinner cast steel with athickness of 100 mm or less may be produced by direct casting. Inaccordance with a conventional method, for example the steel slab ispreferably heated to approximately 1400° C. when containing inhibitorcomponents and is preferably heated to a temperature of 1250° C. or lesswhen not containing inhibitor components. Thereafter, the steel slab issubjected to hot rolling to obtain a hot rolled sheet. When notcontaining inhibitor components, the steel slab may be subjected to hotrolling immediately after casting, without being reheated. Also, a thinslab or thinner cast steel may be hot rolled or may be sent directly tothe next process, skipping hot rolling.

Next, the hot rolled sheet is subjected to hot band annealing asnecessary. This hot band annealing is preferably performed under theconditions of a soaking temperature of 800° C. or higher and 1150° C. orlower and a soaking time of 2 seconds or more and 300 seconds or less.If the soaking temperature is less than 800° C., a band texture formedduring hot rolling remains, which makes it difficult to obtain a primaryrecrystallization texture of uniformly-sized grains and impedes thegrowth of secondary recrystallization. On the other hand, if the soakingtemperature exceeds 1150° C., the grain size after the hot bandannealing becomes too coarse and makes it difficult to obtain a primaryrecrystallized texture of uniformly-sized grains. Furthermore, if thesoaking time is less than 2 seconds, non-recrystallized parts remain anda desirable microstructure might not be obtained. On the other hand, ifthe soaking time exceeds 300 seconds, dissolution of AlN, MnSe, and MnSproceeds, and the effect of the minute amount inhibitor may decrease.

After hot band annealing, the hot rolled sheet is subjected to coldrolling once or, as necessary, cold rolling twice or more withintermediate annealing in between, to obtain a cold rolled sheet with afinal sheet thickness. The intermediate annealing temperature ispreferably 900° C. or higher and is preferably 1200° C. or lower. If theannealing temperature is less than 900° C., the recrystallized grainsbecome smaller and the number of Goss nuclei decreases in the primaryrecrystallized texture, which may cause the magnetic properties todegrade. If the annealing temperature exceeds 1200° C., the grain sizecoarsens too much, as with hot band annealing. In order to change therecrystallization texture and improve magnetic properties, it iseffective to increase the temperature during final cold rolling tobetween 100° C. and 300° C. and to perform aging treatment in a range of100° C. to 300° C. one or multiple times during cold rolling.

Next, the cold rolled sheet is subjected to primary recrystallizationannealing (which also serves as decarburization annealing when includingC in the steel slab) to obtain a primary recrystallized sheet. Anintermediate annealing temperature of 800° C. or higher and 900° C. orlower is effective in terms of decarburization. Furthermore, theatmosphere is preferably a wet atmosphere in terms of decarburization.This does not apply, however, when decarburization is unnecessary. TheGoss nuclei increase if the heating rate to the soaking temperature isfast. Therefore, a heating rate of 50° C./s or higher is preferable. Ifthe heating rate is too fast, however, the primary orientation such as{111}<112> decreases in the primary recrystallized texture. Therefore,the heating rate is preferably 400° C./s or less.

Next, an annealing separator primarily composed of MgO is applied onto asurface of the primary recrystallized sheet and then the primaryrecrystallized sheet is subjected to final annealing for secondaryrecrystallization, to obtain a secondary recrystallized sheet that has aforsterite film on a surface of a steel substrate. The final annealingis preferably held for 20 hours or longer at a temperature of 800° C. orhigher in order to complete secondary recrystallization. Also, the finalannealing is preferably performed at a temperature of approximately1200° C. for forsterite film formation and steel substrate purification.The cooling process after soaking is used to measure the retention timeT from 800° C. to 400° C. and to control the line tension Pr in the nextstep of flattening annealing. If the retention time T is too long,however, the temperature distribution in the coil becomes unbalanced,and the difference between the coolest point and the hottest pointincreases. A difference in thermal expansion then occurs due to thistemperature difference, and a large stress occurs inside the coil,causing the magnetic properties to degrade. Therefore, the retentiontime T needs to exceed 10 hours. In terms of productivity and ofsuppressing diffusion of segregation elements to the grain boundaries,the retention time T is also preferably 80 hours or less.

Furthermore, during cooling of the secondary recrystallized sheet afterthe final annealing, good magnetic properties can be obtained even whenshortening the cooling time by adopting a pattern that holds thesecondary recrystallized sheet for five hours or longer at apredetermined constant temperature from 800° C. to 400° C. The reason isthat unevenness of the temperature distribution within the coil isresolved, and diffusion of segregation elements to the grain boundariescan be suppressed, allowing improvement in the magnetic properties. Theholding at a constant temperature is preferably not performed only once,but rather holding at a constant temperature is preferably repeatedmultiple times while lowering the temperature gradually, as in stepcooling, since unevenness of the temperature distribution within thecoil can be highly resolved.

After final annealing, the secondary recrystallized sheet is preferablywashed with water, brushed, and pickled in order to remove annealingseparator that has adhered. Subsequently, the secondary recrystallizedsheet is subjected to flattening annealing to correct the shape. Theflattening annealing temperature is preferably 750° C. or higher, sinceotherwise the shape adjustment effect is limited. Upon the flatteningannealing temperature exceeding 950° C., however, the secondaryrecrystallized sheet suffers creep deformation during annealing, and themagnetic properties deteriorate significantly. The flattening annealingtemperature is preferably 800° C. or higher and is preferably 900° C. orlower. Also, the shape adjustment effect is poor if the soaking time istoo short, whereas the secondary recrystallized sheet suffers creepdeformation and the magnetic properties deteriorate significantly if thesoaking time is too long. Therefore, the soaking time is set to be 5seconds or longer and 60 seconds or less.

Furthermore, as described above, the line tension Pr (MPa) during theflattening annealing is set to a value of −0.075×T+18 or less inrelation to the retention time T (hr) from 800° C. to 400° C. after thefinal annealing. If the line tension Pr is low, however, meanderingoccurs during sheet passing, and if the line tension Pr is high, thesecondary recrystallized sheet suffers creep deformation and themagnetic properties deteriorate significantly. Therefore, the linetension Pr is set to exceed 5 MPa and to be less than 18 MPa.

For additional reduction in iron loss, it is effective further to applya tension coating onto the grain-oriented electrical steel sheet surfacethat has the forsterite film. Adopting a tension coating applicationmethod, physical vapor deposition, or a method to form a tension coatingby vapor depositing an inorganic material on the steel sheet surfacelayer by chemical vapor deposition is preferable for yielding excellentcoating adhesion and a significant effect of reducing iron loss.

For further reduction in iron loss, magnetic domain refining treatmentmay be performed. A typically performed method may be adopted as atreatment method, such as a method to form a groove in the final productsheet or to introduce thermal strain or impact strain linearly by alaser or an electron beam, or a method to introduce a groove in advancein an intermediate product such as the cold rolled sheet that hasreached the final sheet thickness.

EXAMPLES Example 1

Steel slabs containing, in mass %, C: 0.032%, Si: 3.25%, Mn: 0.06%, N:0.0026%, sol.Al: 0.0095%, Sn: 0.120%, and P: 0.029% were manufactured bycontinuous casting and subjected to slab reheating to 1220° C.Subsequently, the steel slabs were subjected to hot rolling and finishedto a hot rolled sheet with a sheet thickness of 2.7 mm. Thereafter, thehot rolled sheets were subjected to hot band annealing for 30 seconds at1025° C. and then finished to cold rolled sheets with a sheet thicknessof 0.23 mm by cold rolling. Subsequently, the cold rolled sheets weresubjected to primary recrystallization annealing, which also served asdecarburization annealing, for 100 seconds at 840° C. in a 55% H₂/45% N₂wet atmosphere with a dew point of 58° C. to obtain primaryrecrystallized sheets. Subsequently, an annealing separator primarilycomposed of MgO was applied onto a surface of the primary recrystallizedsheets and then the primary recrystallized sheets were subjected tofinal annealing for secondary recrystallization by holding for 5 hoursat 1200° C. in an H₂ atmosphere, to obtain a secondary recrystallizedsheet. At this time, the cooling rate after the final annealing wasvaried to change the retention time T from 800° C. to 400° C. as listedin Table 1.

Next, the secondary recrystallized sheets were subjected to flatteningannealing for 25 seconds at 860° C. At this time, the line tension Prwas changed to a variety of values as listed in Table 1. Next, one sideof each steel sheet was subjected to magnetic domain refining treatment,at an 8 mm pitch, by continuous irradiation of an electron beamperpendicular to the rolling direction. The electron beam was irradiatedunder the conditions of an accelerating voltage of 50 kV, a beam currentof 10 mA, and a scanning rate of 40 m/s.

For the resulting product sheets, the dislocation density was measuredwith a known method, and the iron loss W_(17/50) was measured with themethod prescribed by JIS C2550. The results are shown in Table 1. Table1 shows that good iron loss properties were obtained at conditionswithin the ranges of this disclosure.

TABLE 1 Value of Retention right-hand Line Iron time T (hr) side oftension Dislocation loss from 800° C. Expression Pr density W_(17/50) to400° C. (1) (MPa) (m⁻²) (W/kg) Notes  20 16.5  8 5.0 × 10¹² 0.692Example  20 16.5 12 6.8 × 10¹² 0.713 Example  20 16.5 16 7.7 × 10¹²0.719 Example  40 15.0  8 1.8 × 10¹² 0.687 Example  40 15.0 12 5.9 ×10¹² 0.700 Example  40 15.0 16 1.1  × 10¹³ 0.745 Comparative Example  6013.5  8 4.1 × 10¹² 0.692 Example  60 13.5 12 9.1 × 10¹² 0.715 Example 60 13.5 16 1.2  × 10¹³ 0.742 Comparative Example 100 10.5  8 9.1 × 10¹²0.711 Example 100 10.5 12 1.2  × 10¹³ 0.748 Comparative Example 100 10.516 1.8  × 10¹³ 0.765 Comparative Example Underlined values are outsideof the range of the present disclosure

Component analysis was performed on the steel substrate of the productsheets with the same method as in Experiment 1. As a result, in eachproduct sheet, the C content was reduced to approximately 8 ppm, and theN and sol.Al contents were reduced to less than 4 ppm (below theanalytical limit), whereas Si, Mn, Sn, and P contents were nearlyequivalent to the contents in the slab.

Example 2

A variety of steel slabs containing the components listed in Table 2were manufactured by continuous casting and subjected to slab reheatingto 1380° C. Subsequently, these steel slabs were subjected to hotrolling and finished to hot rolled sheets with a thickness of 2.5 mm.Thereafter, the hot rolled sheets were subjected to hot band annealingfor 30 seconds at 950° C. and then formed to a sheet thickness of 1.7 mmby cold rolling. The hot rolled sheets were then subjected tointermediate annealing for 30 seconds at 1100° C. and then finished tocold rolled sheets with a sheet thickness of 0.23 mm by warm rolling at100° C. Subsequently, the cold rolled sheets were subjected to primaryrecrystallization annealing, which also served as decarburizationannealing, for 100 seconds at 850° C. in a 60% H₂/40% N₂ wet atmospherewith a dew point of 64° C. to obtain primary recrystallized sheets.Subsequently, an annealing separator primarily composed of MgO wasapplied onto a surface of the primary recrystallized sheets and then theprimary recrystallized sheets were subjected to final annealing forsecondary recrystallization by holding for 5 hours at 1200° C. in an H₂atmosphere, to obtain a secondary recrystallized sheet. The retentiontime T from 800° C. to 400° C. after the final annealing was set to 45hours.

Next, the secondary recrystallized sheets were subjected to flatteningannealing for 10 seconds at 835° C. At this time, the line tension Prwas set to 10 MPa, which is within the range of this disclosure. Next,one side of each steel sheet was subjected to magnetic domain refiningtreatment, at a 5 mm pitch, by continuous irradiation of an electronbeam perpendicular to the rolling direction. The electron beam wasirradiated under the conditions of an accelerating voltage of 150 kV, abeam current of 3 mA, and a scanning rate of 120 m/s.

For the resulting product sheets, the dislocation density was measuredwith a known method and was 1.0×10¹³ m⁻² or less for all of the productsheets. Furthermore, the iron loss W_(17/50) was measured with themethod prescribed by JIS C2550. The results are shown in Table 2. Table2 shows that good iron loss properties were obtained at conditionswithin the ranges of this disclosure.

TABLE 2 Iron loss Chemical composition (mass %) W_(17/50) Si Mn Sb Sn MoCu P Other (W/kg) Notes 3.21 0.07 0.071 — — — — — 0.702 Example 3.360.06 — 0.078 — — — — 0.713 Example 3.38 0.07 — — 0.025 — — — 0.715Example 3.35 0.07 — — — 0.039 — — 0.709 Example 3.21 0.10 — — — — 0.051— 0.721 Example 3.20 0.09 0.123 0.036 0.035 0.050 0.011 — 0.690 Example1.77 0.15 0.039 — — — — — 1.535 Comparative Example 3.29 1.53 0.046 — —— — — 2.808 Comparative Example 3.28 0.11 0.051 — — — — C: 0.062 0.698Example 3.25 0.07 0.049 — — — — C: 0.025, Al: 0.024, N: 0.012 0.692Example 3.37 0.08 0.048 — — — — S: 0.004, Cr: 0.05, Bi: 0.020 0.695Example 3.30 0.09 0.048 — — — — Se: 0.016, Ni: 0.06, Te: 0.009 0.700Example 2.98 0.11 0.053 — — — — C: 0.066, Nb: 0.004 0.698 Example 3.110.15 0.039 0.022 0.022 0.075 0.072 C: 0.035, Cr: 0.04 0.675 ExampleUnderlined values are outside of the range of the present disclosure

Component analysis was performed on the steel substrate of the productsheets with the same method as in Experiment 1. As a result, in eachproduct sheet, the C content was reduced to 50 ppm or less, the S, N andsol.Al contents were reduced to less than 4 ppm (below the analyticallimit), and the Se content was reduced to less than 10 ppm (below theanalytical limit), whereas the content of other elements was nearlyequivalent to the content in the slab as listed in Table 2.

Example 3

Steel slabs containing, in mass %, C: 0.058%, Si: 3.68%, Mn: 0.34%, N:0.0011%, sol.Al: 0.0023%, Sb: 0.090%, and P: 0.077% were manufactured bycontinuous casting and subjected to slab reheating to 1220° C.Subsequently, the steel slabs were subjected to hot rolling and finishedto a hot rolled sheet with a sheet thickness of 2.0 mm. Thereafter, thehot rolled sheets were subjected to hot band annealing for 100 secondsat 1060° C. and then finished to cold rolled sheets with a sheetthickness of 0.23 mm by cold rolling. Subsequently, the cold rolledsheets were subjected to primary recrystallization annealing, which alsoserved as decarburization annealing, for 100 seconds at 840° C. in a 55%H₂/45% N₂ wet atmosphere with a dew point of 60° C. to obtain primaryrecrystallized sheets. Subsequently, an annealing separator primarilycomposed of MgO was applied onto a surface of the primary recrystallizedsheets and then the primary recrystallized sheets were subjected tofinal annealing for secondary recrystallization by holding for 5 hoursat 1200° C. in an H₂ atmosphere, to obtain a secondary recrystallizedsheet. One of the following was adopted as the cooling after the finalannealing: cooling without holding at a constant temperature (noholding), cooling by holding for 10 hours at 750° C. (holding once), andcooling by holding for two hours each at 800° C., 700° C., 600° C., and500° C. (holding four times). During holding once and holding fourtimes, the unevenness in temperature inside the coil was resolved.Therefore, as the number of retentions was greater, the cooling rateoutside of the retention was accelerated. As a result, the retentiontime T from 800° C. to 400° C. was 40 hours for no holding, 30 hourswhen holding once, and 20 hours when holding four times.

Next, the secondary recrystallized sheets were subjected to flatteningannealing for 25 seconds at 860° C. At this time, the line tension Prwas changed to a variety of values as listed in Table 3.

For the resulting product sheets, the dislocation density was measuredwith a known method, and the iron loss W_(17/50) was measured with themethod prescribed by JIS C2550. The results are shown in Table 3. Table3 shows that good iron loss properties were obtained at conditionswithin the ranges of this disclosure.

TABLE 3 Retention time T (hr) Value of right-hand Dislocation Iron lossfrom 800° C. side of Expression Line tension density W_(17/50) Coolingmethod to 400° C. (1) Pr (MPa) (m⁻²) (W/kg) Notes No holding 40 15.0  64.9 × 10¹² 0.834 Example No holding 40 15.0 12 6.8 × 10¹² 0.841 ExampleNo holding 40 15.0 18 1.4 × 10¹³ 0.890 Comparative Example Holding once30 15.75  6 4.1 × 10¹² 0.817 Example Holding once 30 15.75 12 4.5 × 10¹²0.824 Example Holding once 30 15.75 18 1.4 × 10¹³ 0.888 ComparativeExample Holding four times 20 16.5  6 2.7 × 10¹² 0.805 Example Holdingfour times 20 16.5 12 3.6 × 10¹² 0.809 Example Holding four times 2016.5 18 1.6 × 10¹³ 0.892 Comparative Example Underlined values areoutside of the range of the present disclosure

Component analysis was performed on the steel substrate of the productsheets with the same method as in Experiment 1. As a result, in eachproduct sheet, the C content was reduced to 10 ppm, and the N and sol.Alcontents were reduced to less than 4 ppm (below the analytical limit),whereas Si, Mn, Sb, and P contents were nearly equivalent to thecontents in the slab.

INDUSTRIAL APPLICABILITY

We can provide a grain-oriented electrical steel sheet with low ironloss even when including at least one of Sb, Sn, Mo, Cu, and P, whichare grain boundary segregation elements, and a method for manufacturingthe same.

The invention claimed is:
 1. A grain-oriented electrical steel sheetcomprising; a steel substrate and a forsterite film on a surface of thesteel substrate, wherein the steel substrate comprises a chemicalcomposition containing, in mass %, Si: 2.0% to 8.0% and Mn: 0.005% to1.0% and at least one of Sb: 0.010% to 0.200%, Sn: 0.010% to 0.200%, Mo:0.010% to 0.200%, Cu: 0.010% to 0.200%, and P: 0.010% to 0.200%, and thebalance being Fe and incidental impurities; and a dislocation densitynear crystal grain boundaries of the steel substrate is 5.0×10¹² m⁻² orless.
 2. The grain-oriented electrical steel sheet of claim 1, whereinthe chemical composition further contains, in mass %, at least one ofNi: 0.010% to 1.50%, Cr: 0.01% to 0.50%, Bi: 0.005% to 0.50%, Te: 0.005%to 0.050%, and Nb: 0.0010% to 0.0100%.
 3. A method for manufacturing agrain-oriented electrical steel sheet, the method comprising, insequence: subjecting a steel slab to hot rolling to obtain a hot rolledsheet, the steel slab comprising a chemical composition containing, inmass %, Si: 2.0% to 8.0% and Mn: 0.005% to 1.0% and at least one of Sb:0.010% to 0.200%, Sn: 0.010% to 0.200%, Mo: 0.010% to 0.200%, Cu: 0.010%to 0.200%, and P: 0.010% to 0.200%, and the balance being Fe andincidental impurities; subjecting the hot rolled sheet to hot bandannealing as required; subjecting the hot rolled sheet to cold rollingonce or cold rolling twice or more with intermediate annealing inbetween, to obtain a cold rolled sheet with a final sheet thickness;subjecting the cold rolled sheet to primary recrystallization annealingto obtain a primary recrystallized sheet; applying an annealingseparator onto a surface of the primary recrystallized sheet and thensubjecting the primary recrystallized sheet to final annealing forsecondary recrystallization, to obtain a secondary recrystallized sheetthat has a forsterite film on a surface of a steel substrate; measuringa retention time T in hr which is a time required after the finalannealing to reduce a temperature of the secondary recrystallized sheetfrom 800° C. to 400° C.; and subjecting the secondary recrystallizedsheet to flattening annealing for 5 seconds or more and 60 seconds orless at a temperature of 750° C. or higher; wherein during theflattening annealing, a line tension Pr in MPa on the secondaryrecrystallized sheet is controlled based on the measured retention timeT in hr to satisfy the following conditional Expression (1), so that adislocation density near crystal grain boundaries of the steel substrateis 5.0×10¹² m⁻² or less:Pr≤−0.075T+18 wherein T>10 and 5<Pr  (1).
 4. The method formanufacturing a grain-oriented electrical steel sheet of claim 3,wherein during cooling of the secondary recrystallized sheet after thefinal annealing, the secondary recrystallized sheet is held for 5 hoursor longer at a predetermined temperature from 800° C. to 400° C.
 5. Themethod for manufacturing a grain-oriented electrical steel sheet ofclaim 3, wherein the chemical composition contains, in mass %, Sb:0.010% to 0.100%, Cu: 0.015% to 0.100%, and P: 0.010% to 0.100%.
 6. Themethod for manufacturing a grain-oriented electrical steel sheet ofclaim 4, wherein the chemical composition contains, in mass %, Sb:0.010% to 0.100%, Cu: 0.015% to 0.100%, and P: 0.010% to 0.100%.
 7. Themethod for manufacturing a grain-oriented electrical steel sheet ofclaim 3, wherein the chemical composition further contains, in mass %,at least one of Ni: 0.010% to 1.50%, Cr: 0.01% to 0.50%, Bi: 0.005% to0.50%, Te: 0.005% to 0.050%, and Nb: 0.0010% to 0.0100%.
 8. The methodfor manufacturing a grain-oriented electrical steel sheet of claim 4,wherein the chemical composition further contains, in mass %, at leastone of Ni: 0.010% to 1.50%, Cr: 0.01% to 0.50%, Bi: 0.005% to 0.50%, Te:0.005% to 0.050%, and Nb: 0.0010% to 0.0100%.
 9. The method formanufacturing a grain-oriented electrical steel sheet of claim 5,wherein the chemical composition further contains, in mass %, at leastone of Ni: 0.010% to 1.50%, Cr: 0.01% to 0.50%, Bi: 0.005% to 0.50%, Te:0.005% to 0.050%, and Nb: 0.0010% to 0.0100%.
 10. The method formanufacturing a grain-oriented electrical steel sheet of claim 6,wherein the chemical composition further contains, in mass %, at leastone of Ni: 0.010% to 1.50%, Cr: 0.01% to 0.50%, Bi: 0.005% to 0.50%, Te:0.005% to 0.050%, and Nb: 0.0010% to 0.0100%.
 11. The method formanufacturing a grain-oriented electrical steel sheet of claim 3,wherein the chemical composition further contains, in mass %, C: 0.010%to 0.100%, Al: 0.01% or less, N: 0.005% or less, S: 0.005% or less, andSe: 0.005% or less.
 12. The method for manufacturing a grain-orientedelectrical steel sheet of claim 4, wherein the chemical compositionfurther contains, in mass %, C: 0.010% to 0.100%, Al: 0.01% or less, N:0.005% or less, S: 0.005% or less, and Se: 0.005% or less.
 13. Themethod for manufacturing a grain-oriented electrical steel sheet ofclaim 5, wherein the chemical composition further contains, in mass %,C: 0.010% to 0.100%, Al: 0.01% or less, N: 0.005% or less, S: 0.005% orless, and Se: 0.005% or less.
 14. The method for manufacturing agrain-oriented electrical steel sheet of claim 7, wherein the chemicalcomposition further contains, in mass %, C: 0.010% to 0.100%, Al: 0.01%or less, N: 0.005% or less, S: 0.005% or less, and Se: 0.005% or less.15. The method for manufacturing a grain-oriented electrical steel sheetof claim 3, wherein the chemical composition further contains, in mass%, C: 0.010% to 0.100%; and at least one of (i) Al: 0.010% to 0.050% andN: 0.003% to 0.020%, and (ii) S: 0.002% to 0.030% and/or Se: 0.003% to0.030%.
 16. The method for manufacturing a grain-oriented electricalsteel sheet of claim 4, wherein the chemical composition furthercontains, in mass %, C: 0.010% to 0.100%; and at least one of (i) Al:0.010% to 0.050% and N: 0.003% to 0.020%, and (ii) S: 0.002% to 0.030%and/or Se: 0.003% to 0.030%.
 17. The method for manufacturing agrain-oriented electrical steel sheet of claim 5, wherein the chemicalcomposition further contains, in mass %, C: 0.010% to 0.100%; and atleast one of (i) Al: 0.010% to 0.050% and N: 0.003% to 0.020%, and (ii)S: 0.002% to 0.030% and/or Se: 0.003% to 0.030%.
 18. The method formanufacturing a grain-oriented electrical steel sheet of claim 7,wherein the chemical composition further contains, in mass %, C: 0.010%to 0.100%; and at least one of (i) Al: 0.010% to 0.050% and N: 0.003% to0.020%, and (ii) S: 0.002% to 0.030% and/or Se: 0.003% to 0.030%.